1. Field of the Invention
The invention relates to a suede-like artificial leather that is excellent in color resistance to light, washing, and dry-cleaning. More specifically, the invention relates to a suede-like artificial leather suitable for use in clothes, shoes and gloves.
2. Description of the Prior Art
Conventional suede-like artificial leather sheets may be obtained by impregnating an entangled nonwoven fabric with a polyurethane solution, coagulating the polyurethane, then napping the surface. Laminating an additional polyurethane layer on the sheet surface results in a grain-imparted artificial leather.
Such artificial leathers however have insufficient light resistance and color fastness to washing. A number of proposals have been made in order to overcome these problems. Among them, for example, Japanese Patent Publication No. 5903/1982 has proposed a method of using a polyurethane composition to which a compound represented by the following formula (1) has been added for improving the polyurethane, which constitutes an artificial leather, thereby overcoming the above-described problems. ##STR1## In formula (1), K represents a hydrogen atom or a benzyl group and R.sub.1 to R.sub.5 each represents a hydrogen atom or a hydrocarbon group.
Japanese Patent Publication No. 43590/1984 has proposed a method of use for an artificial leather a polyurethane composition to which a compound represented by the following formula (2) has been added. ##STR2## In formula (2), R.sub.1 represents a hydrogen atom or a lower aliphatic group, R.sub.2 represents a hydrogen atom or a lower alkyl group, R.sub.3 and R.sub.4 are the same or different and each represents a lower alkyl group and R.sub.5 represents a lower aliphatic group.
In addition, it is known to add a stabilizer to a portion of the raw materials for the preparation of polyurethane, upon preparation of polyurethane, to bind the stabilizer with the polyurethane molecular chain or with the end of the polyurethane molecular chain, thereby improving the properties of polyurethane. For example, method, a method to bind a stabilizer with a hindered amine compound and use it as a portion of the raw materials for polyurethane has been proposed by Japanese Patent Publication Nos. 58469/1982, 51632/1984, 51633/1984, and 49883/1987.
Japanese Patent Publication Laid-Open No. 6097/1986 and Japanese Patent Publication Laid-Open No. 96118/1984 propose incorporating, in addition to the hindered amine, other compounds such as inorganic acid, an organic carboxylic acid, a derivative thereof or a polybasic acid for heightening the improving effects.
Japanese Patent Publication No. 37753/1994 proposes a method in which the surface of a suede-like artificial leather dyed with a metal-complex dye is treated with a hindered phenol compound and hindered amine compound as a light stabilizer.
As described above, incorporating a stabilizer in polyurethane with which a nonwoven fabric is impregnated or coated, or chemically binding a stabilizer with polyurethane have been conventionally adopted in artificial leather to improve the color resistance to light and color fastness to washing.
Many stabilizers however have inferior affinity with polyurethane so that some of these incorporated stabilizers move toward the surface of the polyurethane over time and then fall off the artificial leather, or suffer a change in quality, or fall off owing to the chemical or physical action exerted on them during the steps for preparing artificial leather. More specifically, wet coagulating the polyurethane solution, removing the solvent from the artificial leather by washing, dyeing or finishing, result in a loss in the effects of the stabilizer or color change caused by the deterioration of the stabilizer. Thus, some of the stabilizers sometimes bring about unfavorable conditions.
When an artificial leather is formed of a polyamide fiber, particularly, a microfine polyamide fiber, there is a limitation in the improvement of color resistance to light and color fastness to washing because the fiber itself also involves problems such as yellowing or brittleness. A metal-complex dye having a relatively good dyeing property and color resistance to light is conventionally used. However, when such a dye and a microfine polyamide fiber are used in combination, the resulting artificial leather has inferior color fastness to washing and unclear color; sufficient color variations or excellent color fastness to washing cannot be attained.